NEW YORK — Homeland Security Secretary Janet Napolitano will unveil a new system aimed at highlighting "specific imminent threats" to replace the five color-coded terror alerts.
The system will have two levels of warnings — "elevated" and "imminent" — that will be relayed to the public only under certain circumstances for limited periods of time, sometimes using Facebook and Twitter.
Appearing on NBC's "TODAY" ahead of the official announcement, Napolitano said that the changes were intended to prevent "100 or 120 of these things just stacking up."
Intelligence officials will re-evaluate any threat and "if the information has changed, if the alert no longer needs to exist, it will automatically go away" after a specific period, she added.
However, the warnings may be extended if new information becomes available or as a specific threat evolves.
Agreeing that some people found the current system confusing, Napolitano said the changes aimed to offer specifics on "what to do, what to prepare, what to look for and how to get more information."
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The government has always struggled with how much information it can share with the public about specific threats, sometimes over fears it would reveal classified intelligence or law enforcement efforts to disrupt an unfolding plot. But the color warnings that became one of the government's most visible anti-terrorism programs since the September 2001 attacks were criticized as too vague to be useful and became fodder for late-night talk shows.
"We've been 'orange' since 2006," Napolitano told TODAY. "(The new system) will be specific to geography, to event or incident and it will sunset in two weeks, so we get out of this business of cascading alerts.
"Right now, we have no alerts that would qualify for our standards here. But ultimately if we do, we will issue them via TV, radio ... but also new media as well."
Napolitano also urged Americans to be "situationally aware."
Under the new system, an "elevated threat" alert would warn of a credible terrorist threat against the U.S.
An "imminent threat" alert would be issued in situations involving a credible, specific, and impending terrorist threat against the U.S.
There hasn't been a change in the color warnings since 2006, despite an uptick in attempted attacks and terror plots against the U.S. That's because the counterterrorism community has found other ways to notify relevant people about a particular threat. In December 2010, intelligence officials learned that a terrorist organization was looking to use insulated beverage containers to hide explosives . That information was relayed to the aviation industry to be watchful. Less formal warnings like that will continue under the new system.Video: U.S.: Terrorists may hide explosives in thermoses
The current warning system was introduced nine years ago. The new National Terrorism Advisory System will come into effect on April 26.
Napolitano also told TODAY that she doesn't believe a spate of problems with air traffic control is exposing a potential vulnerability for terrorists.
She said it was important that the Transportation Department and the Federal Aviation Administration conduct an internal review to "look at what's going on in the air traffic community."Video: First lady’s plane has close call (on this page)
Her interview came in the wake of revelations that a jet carrying first lady Michelle Obama to Washington was forced to abort its landing at Andrews Air Force Base , Md., because it came to close to an air cargo plane.
Asked if the Monday incident involving the first lady and reports of sleeping air traffic controllers present an opportunity for terrorists, Napolitano replied, "No, not in that sense."
NBC News, msnbc.com staff and The Associated Press contributed to this report.